3 Answers
3

The most significant difference is that the SB-700 can control flashes that are further away (it has more power and a zoom head) and can be swiveled towards a flash that is at your side. By turning the flash head you can also make sure not to spill controller signal on the scene. Of course, when you have several slave flashes at both sides of camera, you can't use the advantages of swiveling head.

When using the pop-up flash for controller, your SB-700 is free for using as a slave.

Cameras usually disable pop-up flash when there's a flash on hot shoe, so you can't use them both as commanders; is your camera different in this respect?

"Cameras usually disable pop-up flash when there's a flash on hot shoe, so you can't use them both as commanders; is your camera different in this respect?" -- When used wirelessly, I can use both the built-in flash and the popup flash.
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anonOct 27 '11 at 13:30

@anon I honestly don't know if you can use SB-700 in wireless mode as another controller. But it's quite easy to test, just set both your pop-up flash and the SB-700 to commender mode and take a shot with the flash head visible in the frame. If it's lit on the photo, then yes, you could use the SB-700 as a repeater to trigger some other off-camera flash further away or behind a corner; if the flash is off on the photo, the SB-700 does not activate optical sensor in commander mode and acts just like a brick would. Oh, and tell us your results ;)
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ImreOct 28 '11 at 0:09

@mattdm -- Argh, that was a dumb typo. I meant built-in and off-camera =(
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anonOct 28 '11 at 2:39

@anon: in that case I'm still a little confused. The controller has to be attached to the camera to be a controller.
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mattdmOct 28 '11 at 2:43

DO NOT use your Nikon body as the Commander! I had an SU-800 to remotely trigger my flashes, and I sold it when I bought a D7000 thinking it has Commander mode and renders the SU-800 useless. I regretted it so much! The Nikon body will use the pop-up flash, and it will flash once real quick to trigger your off camera flash. What this means is that the pop-up flash becomes another, UNWANTED, source of light, and to a certain distance this just simply ruins a picture. If you're taking your picture from far away, then maybe it won't matter so much. But it really ruined my pictures when trying to take a picture from standard to close-up distances.

What really ticked me off is that the manual book says that the pop-up flash WILL NOT flash, when it fact it does. This is completely false advertising! I have documented this madness here. See for yourself!

In any case your SB-700 has a lot more power and is a much better trigger.

It'a funny you mention this, because I ran into the exact issue you described. I had my camera body's pop-up set to "--" and there was still visible light screwing up my shot! I was confused and frustrated, too.
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anonOct 28 '11 at 2:38

Yeah everyone needs to be aware of this, cause it's a straight up lie!
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rabbidOct 28 '11 at 3:19

The D-7100 documentation acknowledges this and gives three suggestions for mitigating the problem: a) lower ISO, b) small aperture, or c) SG-3IR panel over on-camera flash. They also note that the overall flash compensation affects the flash in Commander mode.
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WayneDec 14 '14 at 16:31

Well, given your comment, I'd say it's better to use the popup as a commander as that allows you to then use your SB-700 as a portable external flash. I have the Canon EOS 60D and a Canon 430EX II which affords the same two configurations.

I've actually just bought a flash pouch for my Lowepro Toploader bag so I can carry my 430EX II on me at all times (my "basic kit" bag in other words). Being able to take that flash off the camera and aim it with your other hand makes party portraits look fantastic.

Here is a recent example of the popup commander on my 60D + 430EX II E-TTL slave held to the camera left in afternoon daylight.